Lord Cuckney, who has died aged 83, operated for nearly half a century in that shadowy area where the secret state, government and the private sector overlap. He started as a spy and moved to become the specialist corporate fixer of first call to governments of every hue.

Mention the names Crown Agents, Westland, Maxwell, Matrix Churchill and Pergau Dam and you have a neat list of most of the main industrial scandals that British governments have had to deal with since the second world war. And in them you have a common thread: John Cuckney was either directly involved in or tangentially linked to them all.

Yet, for a man who played such a central role in some of the stickiest industrial problems of the last half-century, he remained a man of carefully crafted obscurity. His privacy remained intact. Despite a liking for business suits of an extravagantly broad pinstripe, a mop of grey, swept-back hair and distinctively owlish eyebrows, this impressive-looking man had an unshowy, even austere public manner. His private life was a closed book, apart from the fact that he lived in Westminster and Folkestone and that his second wife, Muriel Scott Boyd, exhibited her paintings at the Chelsea Arts Club. For those who asked about his own pastimes, he reserved a few arid dismissals: "stalking yaks" was one of them. He also enjoyed reading about the intelligence service and claimed to have read every word written about Anthony Blunt.

Yet, ironically, if Peter Wright had not used his 1987 book Spycatcher to identify Cuckney as the man who trained him to be a spy, it is conceivable that Cuckney's involvement in MI5, which spanned most of the 1950s, would have remained under wraps. Under wraps, that is, to all those but the people at the heart of Britain's secretive system of governance who later called so frequently on his special skills as a corporate fixer and dealmaker. Others who would have known were those who could decipher his Who's Who entry, which included the illuminating fact that between 1949 and 1957 he was attached to the War Office as "civil assistant, General Staff". This small detail was candid, indeed, not least because the early entries left other less dangerous details of his private life out.

He was born in India, the son of Air Vice-Marshal EJ Cuckney and his wife Lilian. He was educated at Shrewsbury, a school later attended by Michael Heseltine, the minister he would brush up against over the Westland affair. Cuckney then studied medicine at St Andrews University where he nurtured an ambition to become a surgeon. The war intervened. After service with the Royal Northumberland Fusiliers, he returned to St Andrews to read history and economics and then was recruited by the intelligence service.

Wright described Cuckney tellingly in his book as a "tough, no-nonsense" officer who appeared bored with training second-rate operatives and with his sights clearly set on much broader, as it happened, commercial, horizons. He told his trainees that the business of intelligence work was often about "transgressing propriety or the law". The 11th commandment was "thou shalt not get caught".

Subsequently he did not head immediately for the commercial limelight, finding work instead in the City as a stockbroker. First it was Standard Industrial Group, a branch of the Cowdray empire, the establishment organisation which later evolved into S Pearson. In 1961 he became a director of Lazards and in the late 60s became the first director in a century to resign from the merchant bank.

Then he established - with Sir David Alliance, the textiles king of Coats Viyella fame - a bank dedicated to financing trade deals between Britain and the Middle East called Anglo-Eastern. Barbara Castle recruited him to her Railway Policy Review committee in the late 1960s, but it was not until the 1970s that he really branched out into industrial rescue missions. He started with the Mersey Docks and Harbour Company, then moved on to be chief executive of the Property Services Agency, the government's estate managers.

In the mid-1970s, he was parachuted in to pull the Crown Agents out of a £236m black hole. One of his main actions was to hive off International Military Services into a separate Ministry of Defence company which he chaired for 11 years to 1985, even though his tenure at Crown Agents ended in 1978. Then he was lured briefly into trying to turn round the ailing Port of London Authority. But his prescription of closures and heavy redundancies proved too strong a medicine for the then Labour administration facing the 1979 election which brought Margaret Thatcher to power. He left the PLA having been knighted.

The cool and sometimes brutal professionalism with which he tackled one industrial crisis after another earned him a reputation as "the company doctor who never lost a patient". As the 1970s neared their end, Cuckney began to take the first of a long string of directorships which propelled him into the boardrooms of some of Britain's biggest industrial firms including Brooke Bond Tea, John Brown engineering, Royal Insurance, Glaxo, the Midland Bank, Thomas Cook and the venture capital giant 3i.

Untypically, he also dabbled in some corporate buccaneering in the late 1980s takeover boom when he headed a consortium which launched a surprise but short-lived £7bn bid for GEC. This time he was quickly seen off by the wily Arnold Weinstock. Cuckney's Metsun takeover consortium dissolved as quickly as it had emerged. The episode remains a bizarre one and an aberration in Cuckney's career. But his triumphs were not cut and dried. Although his high-profile intervention in 1985 in the fortunes of Westland, Britain's last remaining helicopter manufacturer, achieved survival for the company, it precipitated a political crisis which led to Heseltine and Leon Brittan resigning from the cabinet, and, by her own admission, almost brought down Thatcher.

In industrial terms, the solution for the company that Cuckney pursued with vigour - a tie-up with Sikorsky of the US - never yielded anything but short-term benefits for the company. Heseltine fell on his ministerial sword for a rival solution where Westland would become part of a European combine comprising all of Europe's rival helicopter-makers, including Agusta of Italy.

The Sikorsky tie-up was achieved at great political cost and with the help of a last-ditch spree of mystery share-buying by nominee companies representing Swiss banking interests. In marketing terms, Sikorsky always had more to gain than the ailing West Country firm, for it promised the US firm an inroad into the lucrative Saudi arms market which Britain then dominated.

Ironically, Westland's real future was decided more than a decade later when it agreed a full merger with another helicopter maker. It was Agusta.

But, as in many of Cuckney's interventions, his job was a short-term one. He was a firefighter, a sure hand in a crisis. He enjoyed the trust of governments because he was connected and understood how to solve industrial problems. Fellow industrialists admired his skills, the head of Unilever once describing him as the "best non-executive chairman in the country". He enjoyed the confidence of the City because he worked to a principle of always giving shareholders information - a valuable commodity in the Square Mile.

Armed with these credentials it was not surprising that a grateful government should seek his services again when the Robert Maxwell pensions scandal broke. He was brought in to head a trust to help track down and repay to pensioners some of the hundreds of millions stolen by Maxwell from his businesses and salted away into the tycoon's private accounts in Switzerland and Liechtenstein.

Where Cuckney featured subsequently, it was by association with murkier dealings. He was a director of Midland Bank when it ran a secret unit set up to fund defence sales and which had known links with IMS, the arms trading business Cuckney created from the Crown Agents. The unit counted among its staff Stephen Kock, a man identified as a go-between in the Pergau Dam trade-for-aid affair which eventually saw an indignant Malaysian government suspend trade relations with Britain. Cuckney denied involvement in the Midland's defence sales unit or having ever met Kock.

In the late 1980s, he was chairman of the TI group when it sold Matrix Churchill - the company later at the centre of the Scott inquiry into the sale of arms to Iraq from which Cuckney emerged totally unscathed - to the Iraqi-controlled group TDG. His chairmanship of 3i also coincided with the venture capital group's heavy investment in Astra, the British arms company implicated in the Iraqi supergun affair.

He was made a Conservative peer in 1995. Muriel died in 2004, and he is survived by his third wife, Jane, whom he married in 2007.

• John Graham Cuckney, industrialist and financier, born July 12 1925; died 30 October 2008